Treatment of hides, skins, and pelts



Patented July 24, 1934 1,967,679 TREATMENT OF HIDES, SKINS, AND PELTS Herbert Muench, Hermann Loewe and Luise Birch-Hirschfeld, Mannheim, Germany, assignors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main, Germany No Drawing. Application August 30, 1930, Serial I No. 479,098. In Germany September 12, 1929 20 Claims.

The present invention relates to the treatment of hides, skins, and pelts.

Ithas already been proposed to employ enzymes of animal origin or enzymes from fungi for the 5 bating of pelts or for the bating and unhairing of hides or pelts.-

We have now found that hides," skins or pelts, that is, broadly, hides containing an epidermal layer, including fish skins, can be freed from the said layer and simultaneously bated in one operation in a much more advantageous manner than when using the enzymes hereinbefore specified, by employing therefor enzymes from Carica papaya, or mixtures or juices containing the same. The quantity required of enzyme preparation is at least 0.5 per cent by weight of the soaked; hides, skins or pelts (calculated on the dried juice of unripe fruits of Carica papaya), if no activation has been carried out, i. e. if the enzyme be not employed in activated condition or the hides are not treated in the special manner set out in the following, the quantity may be increased up to 20 per cent or even more. A considerable increase in the enzymatic action can be eflected by activating the enzymes in the usual manner for instance with the aid of very small quantities of hydrocyanic acid, hydrogen sulphide or soluble salts thereof, or with hydrosulphite and in this case the quantity of enzyme employed can be diminished.

The employment of these enzymes is of special advantage, because in alkaline media, even with an abnormally long duration of working and a relatively high concentration of enzymes, practically no attack on the collagen takes place.

The hydrogen ion concentration at which the enzyme action is carried out is' of decisive importance in the treatment of the hides or pelts,

a hydrogen ion concentration of about pH=8 having been found to be the optimum value for the desired action of the said enzymes. Thus for example in a pronounced acid medium their specific action is not every good or none while in an alkaline medium an excellent degradation of the epidermis, or of the parts thereof nearest to the collagen layer, takes place. At an optimal hydrogen ion concentration of about pH=8, a very strong attack on the epidermis, and consequently a loosening of. the hairs, takes place but 'the process may be also carried out at pH down to 8.7 or, preferably between pH=7.2 and pH above 8 and up to about pH=12. Thus, the treat- 'ment may be carried out in strongly alkaline reacting liquids already known for unhairing, for

- 5 example by liming, and also in a slightly acid medium. It is quite contrary to expectation that the enzymes should keep their activity in such alkaline reacting media, as for instance a solution 010.5 gram of caustic soda in each liter of water or a saturated aqueous solution of caustic lime. The unhairing action of the alkalies and the like is considerably assisted by the addition of the enzymes, and at the same time a bating action takes place thus rendering the employment of a special bating bath superfious. 5

This modification allows of a considerable shortening of the liming process, and consequently the valuable constituents of the hide are greatly pro-,- tected. contrasted with the lime-pits hitherto employed, a lime-pit containing papain has the advantage that it unhairs the hides rapidly without the objection of attacking the hide substance by the uncontrollable inflence. of micro-organisms. Also in this case the enzymes are preferably employed in the activated form. The remainders of lime in the unhaired hides may be removed by any usual and convenient manner, for example with the aid of solutions of weak acids, ammonium salts, bisulphite and the like.

In order to maintain the optimal hydrogen ion 0 monium salts, such as mixtures of ammonium 35 chloride and ammonium carbonate. Favourable effects are obtained at temperatures between 15 and 35 C., but also lower temperatures, such as about 6 C. may be applied whereas temperatures above 40 C. should not be applied. When the enzymes are allowed to act on the raw hides for a long period of time, it is of advantage to add a disinfecting agent which does not arrest the enzyme action, for the purpose of preventing the growth of bacteria which would injure the unhaired hides, as for example parachloro metacresol, compounds of arsenic and the like.

The loosening of the epidermal layer and of the hairs may also be substantially assisted by pretreatment of the raw hides with an aqueous no solution of an alkaline agent, a neutral salt or an acid agent such as a weak acid, an alkaline treatment giving very good results; when employing alkaline agents the swelling may be regulated by the addition of neutral salts, such as common salt, Glauber's salt and the like, to the pretreatment bath. Instead of being carried out with alkaline agents or with salts of the said kind, thepretreatment may also be carried out with solutions of weak acids, such as formic acid,

acetic acid, lactic acid and the like,- to which aforesaid neutral salts may be added to regulate any swelling. Since the treatment with enzymes is preferably carried out in an alkaline medium as explained above the acid is removed from the hides by rinsing before the enzymatic actio or, if desired, a treatment in a neutralizing bath, such as a solution of sodium bicarbonate may be effected between the two treatments. The acid pretreatment is especially useful for subsequently assisted by pretreating the hides or the like in a solution of salts highly ionized in aqueous solutions such as the salts of the alkaline bases 1. e. ammonium, alkali metals and the alkaline earth metals including magnesium, as for example the nitrates, bromides, iodides or thiocyanides, preferably of potassium or sodium, or of magnesium or calcium, or mixtures of these, or by carrying out the reaction of the enzymes in the presence of the said salts. The advantages of working in this manner are that the swelling occurring with alkaline or acid agents, can be completely avoided, the hairs are protected to a great extent and substantial improvement in the quality 5 of the hide scrapings for making glue is effected.

The addition of salts during the enzymatic. action does not influence the specific action of the enzymes in any way, but in contrast thereto improves the reaction, so that this treatment may be equally considered as an activation, the effect being, however, probably due to an advantageous influence on the penetration of the enzymes into the hides. A further advantage of this modification of the process according to the present in vention lies in the possibility, by the selection of suitable salts, of excluding the growth of bacteria which would injure the unhaired hides, suitable salts of this nature being the aforesaid salts and further borates or fluorides.

The treatment with salts may be carried out while employing the activated as well as the nonactivated enzymes. l

The said enzymes may also be employed in admixtures with up to 50 per cent thereof of animal enzymes or enzymes from fungi, such as trypsin,

aspergillus proteases, and especially together with enzymes which split fats, such as can be obtained from castor beans, or a treatment with animal enzymes or enzymes from fungi may be carried out before or after the action of vegetable enzymes. The employment of enzymes which split fats is of special importance in the treatment of hides containing large amounts of fat.

All the enzymatic processes described above may be carried out with pastes comprising the ingredients required instead of with baths. Thus for example the enzyme, or juice containing the same, together with the substance adjusting the hydrogen-ion concentration and if desired the activators and/or alkaline or neutral agents may be made into a more or less viscous paste with the aid of any convenient quantity of water and of a finely divided, water-insoluble and solid substance practically or completely inert to the reaction ingredients such as kieselguhr, chalk,

Florida or fullers earth, woodmeal or paper pulp and the like, the paste being then painted onto the hides or skins to be treated.

The following examples will further illustrate the nature of this invention, but the invention is not restricted to these examples. The parts are by weight.

Example 1 ous solution of commercial papain preparation,

which contains 20 parts of papain preparation for each 100 parts of soaked hide, for 48 hours.

After this treatment the skin may be readily unhaired, the grain is smooth and silky and the bating effect excellent.

Example 2 Salted .calfskins are soaked in water for 36 hours and then treated with an aqueous solution of commercial papain preparation activated with about 7/1000 of its weight of hydrocyanic acid. which solution contains 5 parts of activated papain preparation for each 100 parts of soaked hide, after the hydrogen ion concentration of the treatment liquid has been adjusted to pH=8 by phosphates such as mixtures of 9.4 parts of secondary sodium phosphate, and 0.6'part of primary sodium phosphate, the quantity of which is so chosen that-the concentration of the solution is M/10 with reference to the phosphates. After enzymatic action for 3 days the skins may be readily unhaired and the unhaired hides shew an excellent bating effect.

Example 3 Green cow hides are soaked for 24 hours and are then treated for 24 hours with an aqueous M/ 10 ammonium chloride solution of'commercial papain preparation activated with hydro- Example 4 Salted calfskins, after having been soaked for about 24 hours, are treated for 36 hours in a M/2 aquebus solution of potassium bromide, containing- 3 per cent (calculated on the weight of soaked skins) of commercial papain preparation activated with hydrocyanic acid and 0.1 per cent by weight of the solution of para-chlor meta-cresol. The quantity of the bath is about four times the weight of the soaked hides and the hydrogen ion concentration is adjusted to pH=8 with the aid of ammonium salts. The hides obtained readily lose their hair and shew an excellent bating efiect.

Example 5 Well soaked calfskins are treated for about 12 hours with a M/2 aqueous solution of potassium nitrate. After a short rinsing the skins are then placed in an aqueous bath which contains 3 per cent (calculated on the weight of the soaked skins) of commercial papain preparation activated with hydrocyanic acid. The hydrogen ion concentration of the solution is adjusted to pH=8. After action for 24 hours an excellent loosening of the hairs and an excellent bating action are obtained.

Example 6 Dried Balkan sheepskins, after having been soaked for 2 days, are treated for 12 hours in a -M/2 aqueous'solution of sodium nitrate, containing 1 per cent (calculated on the weight of the soaked skins) of commercial papain preparation Example 7 Calfskins, after having been soaked for 24 hours. are placed in a N/20 aqueous solution of caustic soda which contains 0.175 per cent of sodium sulphate. The skins are then transferred to a N/2 aqueous solution of sodium chlorate containing a papain preparation (dried juice of unripe fruits of Carica papaya) in a quantity of 2 per cent by weight of the soaked skins. The hydrogen ion concentration of the bath is adjusted to pH=8 by the addition of ammonium salts. After treatment for 48 hours the loosening of the hairs of the skins is excellent and the skins are well bated. 1

Example 8 Soaked sheepskins are treated for 24 hours with an M/20 solution of formic acid which contains 100 grams of common salt per litre. After having been in an aqueous solution of 4 grams of sodium bicarbonate per litre for'3 Example 9 Soaked sheepskins are treated for gi hours with an M/20 solution offiboricfacid which contains 100 grams of common salt per litre. For the purpose of neutralization the skinsare placed 'in a bath of sodium carbonate and are then treat- ,ed with an aqueous solution having a hydrogen ion concentration of pH='8 which contains 3 per cent (calculated on the weight of soaked skins) of commercial papain preparation, and also 42 grams of sodium nitrate per liter. After 2 days the wool may be readily removed from the skins 'and the latter are excellently bated. The wool has excellent properties.

Example 10 Soaked calfskins are treated with 400 per cent their weight of an aqueous solution of 5 percent (calculated on the weight of soaked skins) of lime (CaO) and 3 per cent of papain preparation activated with a minute quantity of hydrocyanic acid. After treating the skins for 2 days an exaration activated with hydrocyanic acid. After cellent loosening of the hairs is effected. The delimed unhaired hides show an excellent hating effect after tanning.

7 Example 11 Soaked calfskins are treated with 400 per cent their weight of an aqueous solution of 0.5 gram of caustic soda per liter and 3 percent (calculated on the weight of soaked skins) of papain preptreatment for 3 days an excellent loosening of the hairs has taken place, the hides are fallen and show an excellent bating effect.

Example 12 Soaked calfskins are treated with a solution of 1 gram of sodium sulphide per litre and 3 per cent (calculated on the weight of soaked skins) of papain preparation activated with hydrocyanic acid. After 3 days an excellent loosening of the hairs has taken place, and the unhaired hides are fallen and hated.

Example 13 10 kilograms of sodium nitrate, 83.5 grams of secondary sodium phosphate, 4.5 grams of primary sodium phosphate, 50 grams of p-chloro-mcresoi, 500 grams of papain preparation and 5 grams of potassium cyanide are dissolved in 50 liters of water. The solution is incorporated with so much of levigated chalk that a paste is obtained. 100 kilograms of soaked Bulgarian sheep skins are then coated with the paste on their flesh side. After 2 days the skins readily loose the hair and are thoroughly hated, the leather prepared therefrom possessing excellent properties.

. Example 14 100 parts of dried hides of Galloucha fishes are soaked and then treated with 400 parts of a N/2 solution of sodium nitrate which has been incorporated with 1 per centby weight of the soaked hides of an activated papain preparation and the hydrogen-ion concentration of which has been adjusted to pH=8. After from 2 to 3 days the brownish epidermis forming a net-like structure on the surface can be removed by simple brushing, the hides being simultaneously well bated. 125

What we claim is:-

1. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously hating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous dispersion comprising an enzyme preparation of Carica papaya. the quantity of enzyme preparation being at least 0.5 per cent by weight of the soaked hides if no special activation be carried out.

, 2. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous alkaline dispersion comprising an enzyme preparation of Carica papaya at a temperature up to 40 0., the quantity of enzyme preparation being at least 0.5 per cent by weight of the soaked hides if no special activation be carried out.

3. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously hating, which comprises acting at least on the epidermal layer of hides having-such a layer with an aqueous dispersion comprising an enzyme 150 layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on salts, and weak acids, and then with an aqueous up to 40 C. and at a hydrogen-ion concentration between pH=6.7 and pH=12, the quantity of enzyme preparation being at least 0.5 per cent by weight of the soaked hides i1 no special activation be carried out.

4. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer oi! hides having such a layer with an aqueous dispersion comprising an enzyme preparation of Carica papaya and up to 50 per cent thereof of another proteolytic enzyme, at,

a temperature" up to 40 C. and at a hydrogen-ion concentration between pH=6.7 and pH=12, the quantity of enzyme being at least 0.5 per cent by weight of the soaked hides it no special activation be carried out.

5. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous dispersion comprising an enzyme preparation of Carica papaya, at a temperature up to 40 C. in the presence oi. a buffer compound. continuously maintaining the hydrogen-ion concentration of said aqueous dispersion at a value chosen between pH=6.7 and pH=12, the quantity of enzyme preparation being at least 0.5 per cent by weight of the soaked hides if no special activation be carried out.

6. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal-layer or hides having such a layer 'with an aqueous alkaline dispersion comprising an activated papain preparation at a temperature up to 40 C. and at a hydrogen-ion concentration between pH=7.2 and pH=12.

7. The process for degrading the. epidermal ously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous alkaline dispersion comprising a papain preparation and a salt of an alkaline base highly ionized in water. 1

8. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous alkaline dispersion-comprising an activated papain'preparation and a salt of an alkaline base highly ionized in water.

9. The process for degrading the epidermal layer from hides, skins and pelts and simultanethe epidermal layer of hides having such a layer with an aqueous solution of a water-soluble agent, capable of dissociating in water and selected from the group consisting of alkaline agents, neutral alkaline dispersion comprising a papain preparation.

10. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous solution of a neutral, water-soluble salt and 01 a water-soluble agent, capable of dissociating in water and selected from the group consisting of alkaline agents, neutral salts, and

weak acids, and then with an aqueous alkaline dispersion comprising a papain preparation.

11. The process for degrading the epidermal layer from hides, skins and pelts and simultanepreparation of Carica papaya at a temperature.

ously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous solution of a water-soluble agent, capable of dissociating in water and selected from the group consisting of alkaline agents, neutral salts, and'weak acids and then with an aqueous alkaline dispersion comprising an activated papain preparation.

12. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous solution of a neutral, water-soluble salt and of a water-soluble agent, capable of dissociating in water and selected from the group consisting of alkaline agents, neutral salts, and weak acids, and then with an aqueous alkaline dispersion comprising an activated papain preparation.

13. The process for degrading the epidermal layer irom hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous solution of, a water-soluble agent, capable of dissociating in water and selected from the group consisting of alkaline agents, neutral salts, and weak acids, and then with an aqueous alkaline dispersion comprising an activated papain preparation and a salt of an alkaline base highly ionized in water. I

14. The process for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises acting at least on the epidermal layer of hides having such a layer with an aqueous alkaline and viscous paste comprising a papain preparation, a buifer com pound continuously maintaining the hydrogenion concentration of said aqueous paste at pH ,from 1.2 to 12 and a solid, finely divided, practically insoluble and inert substance.

15. A preparation for degrading the epidermal layer from hides, skins and'pelts and simultaneously bating, which comprises a papain preparation, a water-soluble salt of an alkaline base, highly ionized in water, water and a quantity of a buffer compound maintaining the hydrogen-ion concentration of said preparation at pH from 6.7 to 12.

16. A preparation for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises an activated papain preparation, a water-soluble salt of an alkaline base, highly ionized in water, water and a quantity of a buffer compound maintaining the hydrogen-ion concentration of said preparation at pH from 6.7 to 12.

1'7. A preparation for degrading the epidermal layer from hides, skins and p'elts and simultaneously bating, which comprises an activated papain preparation, a neutral, water-soluble salt of an alkaline base, highly ionized in water, water and a quantity of a buffer compound maintaining the hydrogen-ion concentration of said prepa'ration at pH from 1.2 to 12.

18. A preparation for degrading the epidermal layer from hides, skins and pelts and simultaneously bating, which comprises a papain preparation, water, a quantity of a solid, finely divided, practically water-insoluble and inert substance suflicient to render the mixture viscous, and a quantity of a buffer compound maintaining the hydrogen-ion concentration of said preparation at pH from 7.2 to 12.

19. A preparation for degrading the epidermal layer from hides, skins and pelts and simulta- 20. A preparation for degrading the epidermal layer from hides, skins and pelts and simultaneously hating, which comprises an activated papain preparation, an alkali metal nitrate, water, a quantity of a solid, finely divided, practically water-insoluble and inert substance sumcient to render the mixture viscous, and a quantity of a buffer compound maintaining the hydrogen-ion concentration of said preparation at pH from 7.2 to 12.

HERBERT MUENCH. HERMANN LOEWE. LUISE BIRCH-HIR/SCHFELD.

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